Microcrystilline monosodium urate, calcium pyrophosphate and silica adsorb IgG molecules from buffered solutions of Cohn fraction II or from serum. Hyaluronate also adsorbs to urate crystals and can be eluted with IgG. The biological effects of this adsorption (e.g. on polymorphonuclear phagocytosis and chemotaxis), will be determined. The adsorptive phenomena might explain the mechanism by which urate and perhaps other crystals induce an acute inflammatory response. The effects of adsorbed molecules on the ability of urate crystals to affect the platelet release reaction will also be studied. Attempts to remove calcium pyrophosphate (CPPD) crystals from arthritic knees using agents known to promote solubility of synthetic (Ca45) will be made. In vitro nucleation of CPPD will be attempted using animal and human cartilage.